Many methods are employed for environmental remediation in areas contaminated with certain toxicants and/or pollutants. Currently, iron-based treatment is used in cleaning up such compounds as chlorinated solvents (e.g., PCE and TCE), pesticides (e.g., DDT), and heavy metals (e.g., mercury and lead). Adding a secondary metal enhances the reactivity of iron. The second metal serves as a catalyst, and therefore, reduction happens much quicker than with iron alone. However, these catalyst metals themselves are pollutants and very sensitive to the environment of the groundwater they are added to treat, that is, these catalyzed bimetallic zero-valent iron nanoparticles are easily deactivated by groundwater solutes.
In recent years, bulk or nano scale zero-valent iron (ZVI) has received much attention for their potential application for the treatment of contaminated soils and water. Most attention has been focused on their ability as a reductant or adsorbent in the remediation of chlorinated hydrocarbons and heavy metal contaminated groundwater. Chlorinated ethenes, including PCE and TCE, are among the most prevalent contaminants at the US superfund sites.
ZVI-mediated dechlorination under field conditions is relatively slow because, without the addition of catalyst additives, reaction rates are slow and there is a tendency to undergo surface passivation. Therefore, a small amount of catalyst metal, most commonly Ni or Pd, is incorporated. However, bimetallic iron is prone to catalyst deactivation. Additionally, bimetallic iron undergoes rapid iron corrosion in the presence of Pd in an aqueous environment that may result in a lack of treatment longevity and, therefore, lead to a decrease in remediation efficiency.